Davis has spent most of his life in Fentress County, a mostly rural county in the state's coal-mining region. He graduated from Tennessee Technological University in 1966 with a degree in agriculture. Davis, who now lives in the rural Fentress County village of Pall Mall, also owns a construction business, Diversified Construction Co., which builds homes, apartments and offices. Davis and his wife Lynda, an elementary school teacher, have three daughters, Larissa, Lynn and Libby, and five grandchildren.[citation needed]

Davis began his political career in 1978, when he was elected mayor of Byrdstown. Midway through his term as mayor, he was elected to the Tennessee House of Representatives, where he served two terms. He gave up the seat in 1984 to run for the Democratic nomination in the 6th District when Al Gore gave it up to make a successful run for the United States Senate. He narrowly lost the primary to state Democratic Party chairman Bart Gordon. Ten years later, he ran for the Democratic nomination in the 4th District after Jim Cooper gave up the seat to make an unsuccessful run for Gore's Senate seat. He lost narrowly again, this time to one of Cooper's former assistants, Jeff Whorley, who in turn lost the general election to RepublicanVan Hilleary. In 1996, he was elected to the Tennessee State Senate and served two terms there.

While in the Tennessee General Assembly, Davis supported state employee and teacher pay raises, long-term care for senior citizens, character education in schools and new domestic violence legislation. Davis initiated and fought for a bill requiring counseling and a 12-hour holding period for domestic violence offenders.

Midway through his second term in the State Senate, in 2002, Davis ran for the Democratic nomination in the 4th District when four-term Republican incumbent Van Hilleary gave up the seat to make what would ultimately be an unsuccessful run for governor. This time, he narrowly won the primary against a self-funding opponent Fran Marcum of Tullahoma, Tennessee, who spent nearly $2 million in the race. He went on to win a hard fought battle in the general election narrowly defeating Tullahoma Alderman Janice Bowling, who was also Hilleary's district director. He was reelected in a 2004 rematch against Bowling and faced only nominal opposition in 2006 and 2008. Although the 4th is not considered safe for either major party, its size (it stretches across two time zones and five television markets) makes it very difficult to unseat an incumbent.[3]

Davis was a possible candidate for Governor of Tennessee in 2010.[8] However, Davis announced that he had decided not to seek that office in January 2009.[9]

Davis was challenged by Republican nominee Scott DesJarlais. Also on the ballot were Independents Paul H. Curtis, James Gray, Richard S. Johnson, and Gerald York. DesJarlais won 57.1% of the vote to Davis's 38.6%--the third-largest margin of defeat for a Democratic incumbent in the 2010 cycle, and the first time an incumbent had been unseated since the district's creation in 1983.

In the wake of Tennessee passing a strict voter identification law in 2011, Davis was denied the right to vote in Fentress County on Super Tuesday in March 2012. Davis has voted in the county for about fifteen years but was somehow purged from the roll of registered voters.[10]